1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member. More particularly it relates to an electrophotographic photosensitive member having a photosensitive layer containing a resin with a specific structure. The present invention is also concerned with an electrophotographic apparatus, a device unit and a facsimile machine that have such a photosensitive member.
2. Related Background Art
Electrophotographic photosensitive members are, of course, required to be endowed with given sensitivity, potential characteristics and optical properties in accordance with electrophotographic processes applied. In particular, in the case of electrophotographic photosensitive members repeatedly used, they are required to have a durability to the electrical and mechanical external forces that act during electrostatic charging, developing, transfer and cleaning.
Specifically stated, they are required to have a durability against a decrease in sensitivity or dark portion potential caused by O.sub.3 or NO.sub.x generated during corona charging, an increase in residual potential, and wear and scratches caused on their surfaces as a result of sliding friction.
In the case of electrophotographic photosensitive members making use of an organic photoconductive material, their surface layers usually contain resins, and hence the properties of resins are one factor having a great influence on the performance of photosensitive members.
As resins hitherto used in electrophotographic photosensitive members, a bisphenol-A type polycarbonate resin (hereinafter "polycarbonate-A") and a modified polycarbonate resin as disclosed in U.S. Pat. No. 2,999,750 or Japanese Patent Application Laid-open No. 62-187353 have been proposed. These resins, however, have the problems as shown below.
(1) The resins have such poor solubility that they exhibit good solubility only in a few kinds of halogenated aliphatic hydrocarbons, such as dichloromethane and 1,2-dichloroethane. These halogenated aliphatic hydrocarbons have a low boiling point. Hence, photosensitive members manufactured by the use of a coating solution prepared using any of these solvents tend to have whitened coating surfaces. In addition, use of such solvents requires troublesome process management such that the solid's content in coating solutions must be kept constant.
(2) With regard to solvents other than the halogenated aliphatic hydrocarbons, the resins are partly soluble in tetrahydrofuran, dioxane, cyclohexane, or a mixed solvent of these. The solutions obtained, however, have poor stability with time such that they may gel in a few days.
Use of bisphenol-Z type polycarbonate resins (hereinafter "polycarbonate-Z") has settled these problems. However, in recent years, as image quality, durability and productivity are increasingly made higher in the field of electrophotography, resins are being studied which can satisfy the required properties at a much higher level.